Currently in the field of ophthalmology and optometry, automated systems are used to control auto-phoropters, chart projectors, and other equipment providing increased efficiency in the exam, including the capture and transfer of data to electronic medical records. Chart projectors are limited in their use, however, as they have a finite number of tests available, require considerable maintenance and cannot present randomized eye charts. Since the automated phoropters are new technology and relatively expensive, practitioners often objected to using older outdated chart projectors in combination with more sophisticated new technology. There also exists a strong movement in the industry to migrate away from chart projectors in favor of more sophisticated computerized visual acuity systems, and a resulting need for the integration between auto-phoropters, computerized visual acuity and other equipment.
Currently available auto-phoropters include: RT-5100 Auto-Phoropter sold by MARCO of Jacksonville, Fla. and made by NIDEK of Japan; RT-2100 Auto-Phoropter sold by MARCO Jacksonville, Fla. and made by NIDEK of Japan; and, CV-5000 sold by TOPCON of Japan. In addition, currently available automated visual acuity testing systems include the PROVIDEO® sold by Innova Systems, Inc. of Burr Ridge, Ill.
In addition to the above, for clinical trials on many new ophthalmic products, particularly those requiring contrast sensitivity testing, the FDA requires vision analysis to be conducted at both photopic and mesopic light levels. In some cases, scotopic levels are also required. Photopic levels are high light levels where primarily the cones of the retina are the primary light receptors. Mesopic levels are low-intermediate light levels where both the rods and cones of the retina serve as the light receptors. Scotopic levels are very dim conditions where only the rods of the retina serve as the light receptors.
The requirements for many vision tests are very precise and require specific light levels of 85 candela per square meter for photopic measurement; 3-4 candela per square meter for mesopic measurement; and less than 2 candela per square meter for scotopic levels.
With traditional vision testing methods, these levels were achieved by either controlling the illumination of a vision testing chart or by controlling the luminance of a light box device. With computerized vision testing, it is not possible to accurately produce these light levels in a consistent, repeatable manner using a standard CRT or LCD monitor.
One problem associated with the difficulty achieving correct light levels is the inability to produce the many shades of grey required for contrast testing if the light output of the monitor is reduced. The brightness of the monitor may not be used to control the light level, because the quality of the image is reduced with reduced brightness and it is very tedious to restore the monitor to its original settings for subsequent tests. Reducing the light level by making the background a darker shade of grey reduces the number of grey shades available for test optotypes by 255 minus the value of the grey shade used for the background. The obvious solution of placing a filter over the monitor screen is inadequate because of the lack of accurate, stable filter densities and the difficulty of calibrating the monitor/filter combination to the correct light level.